The invention relates to a process for coating fibrous glass with glass metal. More particularly, the invention concerns a method by which a glass metal coating can be applied to a fibrous glass electrochemically, under conditions free of current. The amorphous glass metal coating inhibits the corrosion of the fibrous glass in an alkaline medium and improves its mechanical properties.
The term "fibrous glass" as used throughout the specification and claims includes glass-cloth, glass-staple and glass-quilt.
Fibrous glasses are widely used for reinforcing synthetic materials. By incorporating a highly elastic fibrous glass, which has a high breaking strength, into a synthetic material, products with excellent mechanical properties can be obtained. Under alkaline conditions, however, the fibrous glass is strongly deteriorated causing the reinforcing effect of the fibers entirely cease within a relatively short time. Therefore such glass fibers cannot be used for reinforcing cement-bonded products.
Cement-bonded products reinforced with fibrous glass can for example be used in aboveground constructions, e.g. for manufacturing front panels, steady frameworks, false ceilings; and in civil engineering uses, for example, for covering underground pipe-lines, manufacturing pile-planks and small constructive works. Alkali-resistant fibrous glasses can be employed for producing so-called glass cement products. Alkali-resistant fibrous glasses are rather expensive and after a certain time their reinforcing effect decreases rapidly. Generally the breaking strength of glass cement products decreases to half of its original value within 10 years.
A method of producing metal coatings on the surface of objects made of synthetic materials is disclosed in British patent specification No. 1,175,348. According to this patent a nickel alloy is deposited from an aqueous solution onto the surface of synthetic materials and then a copper or chromium coating is applied to the nickel alloy layer by conventional electrolytic techniques.
Further methods of producing nickel coatings on glass surface are disclosed in British patent specification No. 1,094,318 and in U.S. Pat. Nos. 3,476,594 and 3,686,020. Before coating, the glass surface is etched with an aqueous solution of hydrogen fluoride or a mixture of hydrogen fluoride and chromium trioxide. The pretreated, rough glass surface is then treated in an aqueous bath containing nickel sulfate and sodium hypophosphite or nickel fluoroborate, nickel sulfate and sodium hypophosphite and optionally further additives. In this way a crystalline nickel-phosphorus coating is formed on the glass surface. According to this method highly corrosive chemicals are used for treating the glass surface before coating and the quality of the metal coatings formed is not always satisfactory.
Glass metals, e.g. amorphous nickel, can be formed on metal surfaces by the so called Kanigen method ("Catalytic Nickel Generation," General American Transportation Corporation; see e.g. Gepgyartastechnologia, November 1975). This method can, however, be employed for coating glass surfaces only after a careful chemical and catalytic pre-treatment of the substrate.
It can generally be established that the deposition of nickel or other similar glass metal coatings on metals from baths containing a catalyst as a promotor and a stabilizator, under conditions free of current, is initiated by the metal to be coated. Under different conditions a metal, e.g. nickel layer, is precipitated not only on the substrate to be coated but also on the walls of the containers, pipe-lines, pumps, heating system, etc. and therefore the coating bath is inactivated rapidly.